"Her gün spor yapmalısın."
Translation:You must play sports every day.
As far as I know (as a non-native speaker of English), (in the US and in the UK) "sports" is used for general sporting activities and "sport" is used for a single sporting activity. Am I wrong?
I'm a native UK English speaker, so can confirm that the use of sports as the collective noun is specific to US English. It's actually come up on the Duolingo forums before as an issue. In UK English, you only use the plural 1) to refer to multiple different sports (e.g. "rugby, tennis, and football are all sports") or 2) as the modifier of a noun (e.g. "I won the 100m at sports day", "I drive a sports car") - see here. An example combining both uses would be, "I like to watch sport on the sports channel". In any case, the point is that both are right so both should be accepted.
On another question, "Okulda spor yoktur", 'sport' if allowed, so it seems like the rejection here is just an oversight.